Dealing With Uncertainty of Micro Gears: Integration of Dimensional Measurement, Virtual and Physical Testing

Design and quality assurance of micro gear wheels and involute gear wheels involve multiple challenges regarding prediction of functionality and life cycle performance of complex and wear-resistant micromechanical systems. First of all, this is due to the fact that up to now no tolerance system for micro dimension has been defined. In second place, most measurement strategies for the dimensional characterization of involute micro gears cannot be brought forward from the macro world just as they are. There is few knowledge about the relevant quality characteristics for these micro systems, optical sensors’ precision is affected by fuzzy edges detection and no tactile scanning modes for relevant features smaller than 100 μm exist, which is the scale normally applied in macroscopic dimensions. Simulation methods for analyzing the influence on the whole system of different components’ geometrical deviations are very valuable to supplement the knowledge based on real tests. Furthermore, it could be also necessary to consider the material’s anisotropy caused by the not negligible grain structure to evaluate the stress field correctly. Therefore, a new approach for design and quality assurance needs to be developed, in order to assure the functionality and long-term performance of molded micro systems. This work uses a planetary gear train as a demonstrator. A validation of the entire product functionality test chain has to be conducted to come closer to an integrated robust design approach for mechanical micro systems — from simulation in the early design stages to test and to quality assurance of large series production. This paper outlines a threefold methodological approach integrating dimensional measurement, virtual tests based on real geometry and physical tests of real gears. The measurement of the micro systems components both in disassembled as in assembled state is conducted using multisensory coordinate measurement machines. Based on the measured contours of real gears, virtual gears are derived and meshed for its subsequent use in adequate FEA model. Simultaneously, the gears are mounted and tested on a micro gear test rig. Both simulation and test rig conduct a radial composite inspection adapted to the micro scale; results are then compared. Micro gears molded of zirconium oxide were selected as a demonstrator for the presented methodology. These 12 teeth gears, with a diameter of approximately 2.0 mm and a modulus of 169 μm, are produced within Collaborative Research Center (CRC) 499 “Development, Production and Quality Assurance of Primary-Shaped Micro Parts made of Metallic and Ceramic Materials” of the German Research Foundation (DFG).